The present invention relates to solar powered lighting systems principally for outdoor illumination. More particularly, the invention relates to solar powered lighting systems and/or solar power alarm systems which require the sensing of low background light level in conjunction with the detection of an emitted long wavelength radiation before activation.
Solar powered lighting systems have been known in the art for some time and are readily available in the marketplace for outdoor lighting purposes. Basically, and as disclosed in U.S. Pat. No. 4,835,664 to Hung-Sheng Wen, they are comprised of one or more photovoltaic cells which are used to charge a battery. The battery in turn powers a light source; the circuit being activated upon the sensing by a photocell of a low background light level. The battery keeps the light source illuminating until the battery is drained (e.g. usually within three to four hours).
The solar powered lighting systems of the art have been limited commercial success due to the limitations of such systems. In order to be at aIl feasible in a cost sense, the number of photovoltaic cells utilized must be kept small. Typical systems presently available are capable of storing about ten watt-hours of power. Thus, in order for the battery to power the light source upon nightfall, and to provide for the situation of cloudy days restricting power collection, the light source must be kept small; on the order of 1/10-1 watt. Such lighting, however, is often considered insufficient, even for path lighting. Also, in winter and in climates with less sunlight, the amount of power available is even smaller. Thus, when the nighttime hours are increased and the light is the most needed, the systems of the present state of the art are incapable of providing sufficient lighting.
Very recently, in an advertisement in Popular Science Magazine, October 1989, p. 86, a solar powered light system was disclosed utilizing an infrared sensor for controlling when the light source is to be turned on and off, thereby using the power only when needed. The advertisement, however, is not prior art to this invention, as the invention was conceived and reduced to practice in advance of the appearance of the advertisement.
Examples of relevant patents which are prior art to this invention include:
______________________________________ Patent # Inventor Patent # Inventor ______________________________________ 3,459,961 Ravas 4,539,516 Thompson 4,186,388 Robinson 4,772,990 Linehan et al. 4,314,198 Rogers 4,701,693 Nishimura 4,433,328 Saphir et al. 4,804,858 Jorlov et al. 4,450,351 Fraden 4,835,664 Wen 4,486,820 Baba et al. 4,843,525 Williams ______________________________________
However, none of these patents overcome the significant problems regarding the power requirements for desired illumination.